National Parks officers said today that the calf, which hasn't eaten at least since Sunday when it was first spotted, could be put down depending on the results of the test.

National Parks Sydney North Regional manager Chris McIntosh said he had not given up hope, but "the prognosis is pretty grim".

Advertisement

He said measures such as feeding the whale through a tube or trying to raise it in captivity, as has been done at California's Sea World, were not possible in Australia and were unlikely to work in this case.

"When they did that in California, they had an 11-million litre tank that they [partially drained every two hours]," he said.

The draining was necessary to filter out surplus food which was not consumed by the whale.

"They had 30 people working around the clock and they force fed the whale with a massive tube. Not only do we not have the facilities to do that in NSW, but the success rate of that method is only 2 to 3 per cent and it has never been tried on a humpback whale.

"It is likely only to distress or endanger the whale and to endanger those trying to carry out the feeding process."

National Parks and Wildlife Service spokesman John Dengate said the whale's only remaining hope of survival was for it to communicate with and then swim out to other humpbacks off the Sydney coast, or for its mother to return.

A number of whale pods have been spotted off the coast today but they are either of the wrong species or did not stop to communicate with the abandoned calf.

"Unfortunately those options are both extremely unlikely," Mr Dengate said.

With most baby humpbacks only able to survive for five to seven days after separation from the mother, time is running out.

Mr McIntosh said in the event that the whale had to be put down it would be injected with "a large volume" of anaesthetic, possibly after it had beached.

He said this would be a quick and painless way for the whale to die.

Loading

He would not be drawn on a time frame but said this afternoon's blood test would be critical.

The blood test will involve National Parks officers drawing blood from a vein on the tail fins of the whale. The test will indicate the whale's stress levels and general physical condition and remaining strength.